1. Field of the Invention
The subject matter disclosed generally relates to the field of semiconductor image sensors.
2. Background Information
Photographic equipment such as digital cameras and digital camcorders contain electronic image sensors that capture light for processing into a still or video image, respectively. There are two primary types of electronic image sensors, charge coupled devices (CCDs) and complimentary metal oxide semiconductor (CMOS) sensors. CCD image sensors have relatively high signal to noise ratios (SNR) that provide quality images. Additionally, CCDs can be fabricated to have pixel arrays that are relatively small while conforming with most camera and video resolution requirements. A pixel is the smallest discrete element of an image. For these reasons, CCDs are used in most commercially available cameras and camcorders.
CMOS sensors are faster and consume less power than CCD devices. Additionally, CMOS fabrication processes are used to make many types of integrated circuits. Consequently, there is a greater abundance of manufacturing capacity for CMOS sensors than CCD sensors.
To date there has not been developed a CMOS sensor that has the same SNR and pixel pitch requirements as commercially available CCD sensors. Pixel pitch is the space between the centers of adjacent pixels. It would be desirable to provide a CMOS sensor that has relatively high SNR while providing a commercially acceptable pixel pitch.
The image sensor is typically connected to an external processor and external memory. The external memory stores data from the image sensor. The processor processes the stored data. To improve picture quality it is sometimes desirable to capture two different images of the same picture. With CCD sensors there is an inherent delay between capturing the first image and capturing the second image. The image may move during this delay. This image movement may degrade the quality of the resultant picture. It would be desirable to decrease the time required to capture and transmit images from the pixel array. It would also be desirable to provide a low noise, high speed, high resolution image sensor that can utilize external memory.